Telecommunications systems and methods transport information for applications that have different performance requirements. For example, interactive real-time applications, such as voice over Internet protocol (VoIP) and video telephony (VT), have strict end-to-end delay and delay jitter requirements. With VoIP, for example, an end-to-end delay less than 150 milliseconds (ms) may not be perceived by a human ear, delay between 150 and 300 ms may be perceptible but ideal, and delay exceeding 300 ms may be unacceptable and hinder the interactivity possible in voice communications. Therefore, a network may be configured to disregard packets having a delay greater than a selected threshold. Such a configuration may lead to packet loss and a further degradation of the network quality.
End-to-end delay of packets in a network may be caused by transmission delays and/or queuing delays in routers and/or other components of the network that process the packets. Delay jitter in the network may be caused by the variation in delay experienced by individual packets. Because of delay jitter, packets may be received in an order different than the order in which the packets were input into the network. To address these issues, conventional systems and methods may be designed to buffer packets for longer periods of time, thereby reducing the effects of delay jitter, because packets can be received and re-ordered prior to playback at the receiver. The drawback to this approach is excessive end-to-end delay. One approach is to buffer packets for shorter periods of time to maintain acceptable end-to-end delay. The drawback to this approach is that the effects of delay jitter may not be removed.
Accordingly, conventional systems and methods may disadvantageously degrade the quality of the application due to lost packets or extensive buffering to attempt to capture delayed packets. Accordingly, these systems may not meet delay performance requirements and/or may experience severe degradation in the communication due to an extensive number of lost packets.
One exemplary conventional system and method of addressing end-to-end delay and delay jitter is the maximum delay variation (MDV) method. The conventional MDV method may remove delay jitter by buffering the packets at their destination for the duration of maximum delay variation, which is defined as the constant value that is the difference between the maximum delay of the packets and the minimum delay of the packets in a single data session. As used herein, the term “data session” means a voice call or video or other communication session from beginning to end. While the conventional MDV method may be used to remove the de-sequencing effect of delay jitter completely, the time for which the packets are buffered may be greater than necessary, thereby causing unnecessary delay before playback of the packets at the receiver. The unnecessary delay may cause end-to-end delay to be greater than allowed for interactive real-time applications such as VoIP and VT.